import java.security.Key;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.HashMap;
import java.util.Map;
import javax.crypto.Cipher;
import javax.crypto.KeyAgreement;
import javax.crypto.SecretKey;
import javax.crypto.interfaces.DHPrivateKey;
import javax.crypto.interfaces.DHPublicKey;
import javax.crypto.spec.DHParameterSpec;
import javax.crypto.spec.SecretKeySpec;


public abstract class DHCoder {
    /**

     * 非对称加密密钥算法

     */
    private static final String KEY_ALGORITHM = "DH";
    /**

     * 本地密钥算法，即对称加密密钥算法

     * 可选DES、DESede或者AES

     */
    private static final String SELECT_ALGORITHM = "AES";
    /**

     * 密钥长度

     */
    private static final int KEY_SIZE = 512;
    //公钥

    private static final String PUBLIC_KEY = "DHPublicKey";
    //私钥

    private static final String PRIVATE_KEY = "DHPrivateKey";

    /**

     * 初始化甲方密钥

     * @return Map 甲方密钥Map

     * @throws Exception

     */
    public static Map<String, Object> initKey() throws Exception{
        //实例化密钥对生成器

        KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance(KEY_ALGORITHM);
        //初始化密钥对生成器

        keyPairGenerator.initialize(KEY_SIZE);
        //生成密钥对

        KeyPair keyPair = keyPairGenerator.generateKeyPair();
        //甲方公钥

        DHPublicKey publicKey = (DHPublicKey)keyPair.getPublic();
        //甲方私钥

        DHPrivateKey privateKey = (DHPrivateKey)keyPair.getPrivate();
        //将密钥对存储在Map中

        Map<String, Object> keyMap = new HashMap<String, Object>(2);
        keyMap.put(PUBLIC_KEY, publicKey);
        keyMap.put(PRIVATE_KEY, privateKey);
        return keyMap;
    }

    /**

     * 初始化乙方密钥

     * @param key 甲方公钥

     * @return Map 乙方密钥Map

     * @throws Exception

     */
    public static Map<String, Object> initKey(byte[] key) throws Exception{
        //解析甲方公钥

        //转换公钥材料

        X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(key);
        //实例化密钥工厂

        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        //产生公钥

        PublicKey pubKey = keyFactory.generatePublic(x509KeySpec);
        //由甲方公钥构建乙方密钥

        DHParameterSpec dhParameterSpec = ((DHPublicKey)pubKey).getParams();
        //实例化密钥对生成器

        KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance(KEY_ALGORITHM);
        //初始化密钥对生成器

        keyPairGenerator.initialize(KEY_SIZE);
        //产生密钥对

        KeyPair keyPair = keyPairGenerator.generateKeyPair();
        //乙方公钥

        DHPublicKey publicKey = (DHPublicKey) keyPair.getPublic();
        //乙方私约

        DHPrivateKey privateKey = (DHPrivateKey) keyPair.getPrivate();
        //将密钥对存储在Map中

        Map<String, Object> keyMap = new HashMap<String, Object>(2);
        keyMap.put(PUBLIC_KEY, publicKey);
        keyMap.put(PRIVATE_KEY, privateKey);
        return keyMap;
    }

    /**

     * 加密

     * @param data 待加密数据

     * @param key 密钥

     * @return byte[] 加密数据

     * @throws Exception

     */
    public static byte[] encrypt(byte[] data, byte[] key) throws Exception{
        //生成本地密钥

        SecretKey secretKey = new SecretKeySpec(key, SELECT_ALGORITHM);
        //数据加密

        Cipher cipher = Cipher.getInstance(secretKey.getAlgorithm());
        cipher.init(Cipher.ENCRYPT_MODE, secretKey);
        return cipher.doFinal(data);
    }

    /**

     * 解密

     * @param data 待解密数据

     * @param key 密钥

     * @return byte[] 解密数据

     * @throws Exception

     */
    public static byte[] decrypt(byte[] data, byte[] key) throws Exception{
        //生成本地密钥

        SecretKey secretKey = new SecretKeySpec(key, SELECT_ALGORITHM);
        //数据揭秘

        Cipher cipher = Cipher.getInstance(secretKey.getAlgorithm());
        cipher.init(Cipher.DECRYPT_MODE, secretKey);
        return cipher.doFinal(data);
    }

    /**

     * 构建密钥

     * @param publicKey 公钥

     * @param privateKey 私钥

     * @return byte[] 本地密钥

     * @throws Exception

     */
    public static byte[] getSecretKey(byte[] publicKey, byte[] privateKey) throws Exception{
        //实例化密钥工厂

        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        //初始化公钥

        //密钥材料转换

        X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(publicKey);
        //产生公钥

        PublicKey pubKey = keyFactory.generatePublic(x509KeySpec);
        //初始化私钥

        //密钥材料转换

        PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(privateKey);
        //产生私钥

        PrivateKey priKey = keyFactory.generatePrivate(pkcs8KeySpec);
        //实例化

        KeyAgreement keyAgree = KeyAgreement.getInstance(keyFactory.getAlgorithm());
        //初始化

        keyAgree.init(priKey);
        keyAgree.doPhase(pubKey, true);
        //生成本地密钥

        SecretKey secretKey = keyAgree.generateSecret(SELECT_ALGORITHM);
        return secretKey.getEncoded();
    }

    /**

     * 取得私钥

     * @param keyMap 密钥Map

     * @return byte[] 私钥

     * @throws Exception

     */
    public static byte[] getPrivateKey(Map<String, Object> keyMap) throws Exception{
        Key key = (Key) keyMap.get(PRIVATE_KEY);
        return key.getEncoded();
    }

    /**

     * 取得公钥

     * @param keyMap 密钥Map

     * @return byte[] 公钥

     * @throws Exception

     */
    public static byte[] getPublicKey(Map<String, Object> keyMap) throws Exception{
        Key key = (Key) keyMap.get(PUBLIC_KEY);
        return key.getEncoded();
    }
}